(I) Field of the Invention
This invention relates to the separation of solids from vapor/solid mixtures. More particularly, this invention relates to ballistic separations of solids from mixtures of vapors and solid particles having particle size distributions in the range of about 0 to 200 microns.
(II) Prior Art
The two main methods of separating particulate matter from mixtures of vapors and particles are ballistic separations and cyclonic separations. Ballistic separation involves diverting from a mixture of particulates and vapors moving in a substantially straight line a stream of vapors at an angle transverse to the mixture. In the ballistic separation there is substantially no change in the relative velocity of the solids versus that velocity of the mixture of solids and vapors just prior to separation of a transverse stream consisting of a vapor containing far less particulates than was in the original mixture. Cyclonic separation, on the other hand, involves an acceleration, i.e., a change in velocity, of a mixture of solid particulates and vapors, wherein because of the difference in mass of the solid particulates versus the vapors there is a tendency to concentrate particulate components in one stream and to concentrate the vapors in a different stream both of which streams are being accelerated. One way to induce the acceleration of a mixture is to cause it to move along a wall which is curved. Typically cyclones have cyclonic retaining walls which cause mixtures of vapors and solids to move in a curved path.
In U.S. Pat. No. 1,600,762 (1926) of C. G. Hawley, there is disclosed an apparatus and process for separating carrier fluids from a mixture of the carrier fluid and entrained substances. The mixture referred to as a burdened carrier is accelerated in a container thereby causing the entrained material to be concentrated along a wall and then by force of gravity to be carried down into a lower portion of the container and the carrier portion is caused to double back on itself and through at least a portion of the accelerated burdened carrier out through an exit. This disclosed method in the terminology given herein before is employing a cyclonic type of separation. The centrifugal separation of the foreign substances is established by and within the vortex created by swirling the burdened carrier mass. Due to the differences in inertia between the entrained substances and the fluid carrier there is a separation or a concentration of the entrained material against the wall of the containing vessel. In the patent, the vessel is referred to as a shell or casing within which the acceleration is induced.
In U.S. Pat. No. 1,746,253 (1930) of C. G. Hawley, there is disclosed an improved apparatus and method for separating particulate matter or entrained substances from carrier fluids. In the apparatus and process, an incoming carrier stream is projected downwardly and at a point deflected laterally and thence downward and thence inward. Part of the stream consisting of the separated foreign substances by the force of gravity moves downward into an accumulation space within a separator and another part of the carrier stream having a reduced particulate component is caused to move against and deflect a portion of the burdened (particulate containing) stream. The burdened stream with particulate and fluid matter acts as a filter for the escaping stream consisting of primarily fluid matter. Also disclosed is a method of inducing the burdened carrier, i.e. the mixture of fluid and entrained substances, to move downward and in a helical path which causes the burdened fluid to accelerate against a deflecting path concentrating the particulate matter entrained within the fluid against the wall and inducing the fluid portion to move back upon itself and move against the cyclonic movement or helical movement of the burdened fluid through and then away from the burdened fluid. The method and apparatus disclosed in U.S. Pat. No. 1,746,253 is according to the definition herein above given a cyclonic separation, because the mixture of vapor and solids, i.e. the burdened fluid causes a change in velocity component of the mixture (both particulates and vapors) prior to separation.
In U.S. Pat. No. 4,066,533 of Myers et al, there is disclosed a method for disengaging catalyst particles from the effluent of a riser tube of a fluid catalytic cracking unit. The improved method for effecting the separation of catalyst particles from hydrocarbon conversion products involves actually discharging the bulk of the catalyst as a mixture of both catalyst and hydrocarbon conversion products in a substantially linear concurrent flow stream and then diverting laterally into a cyclonic separation system a stream consisting substantially of vapors only having a much lower concentration of particles contained therein than was present in the original axially flowing mixture of vapors and solids. The method for diverting laterally into a cyclonic separation system involves having a cyclonic separation system directly communicating with a conduit or tube such as used in a riser cracker. Examples of riser crackers can be found in U.S. Pat. No. 4,066,533. Transport velocities disclosed to occur in the operation of a typical fluid catalytic cracker are on the order of from 35 to 50 feet per second. The main criteria for transport velocities is that they be sufficient to impart a sufficient momentum to the solid particles within a mixture of solid particles in vapors flowing in a riser so that the solid particles will have a sufficient tendency to both stay in a straight line, and having left the riser will tend to ricochet from the walls of a retaining chamber away from the opening of the riser so as not to fall back into the riser. A deflector cone is disclosed to prevent particulates from either abraiding the upper end of a disengaging vessel or reentering the riser tube. A second deflector upstream of the radial takeoff point which leads to the cyclonic separation means is also separately disclosed. this second deflector extends angularly inward from the side of a riser wall just upstream of the side wall port leading to the cyclinic separation system. It has a tendency to deflect catalyst away from the port so as to increase the concentration of vapor versus particulate solids that would otherwise be drawn through the takeoff port into the cyclonic separation system.
In U.S. Pat. No. 4,070,159 (1978) of George D. Myers et al, there is disclosed an apparatus for the removal of solid particulates from gaseous mixtures of particulates and vapors. The apparatus broadly comprises a disengaging chamber, an elongated tubular conduit, a means for effecting the flow of a gas-solid stream; and a cyclone separator having a inlet laterally communicating with the elongated tubular conduit near the downstream end of the conduit. The downstream axial opening of the elongated tubular conduit is adapted to permit initial flow of the particulates into the disengaging chamber. Essentially, the apparatus is designed to carry out what has been defined to be a ballistic separation. Also disclosed in this patent is the use of a baffle or deflector means upstream of the opening in the elongated tubular conduit which is in direct communication with the cyclone separator means. Also disclosed is the possibility of having either a uniform diameter throughout the elongated tubular conduit or have a tapered section disposed at one end of the tubular conduit to increase the disengagement of the catalyst from the gas stream by accelerating linearly the mixture of gas and particulate matter. The separation carried out by the separator means results in a stream of vapors which are taken out of the disengaging chamber and the particulate matter returned to a lower portion of the disengaging chamber. The transport velocities in the elongated tubular conduit are disclosed to be in the range of from about 35 to 50 feet per second. The cracking catalyst applicable is usually in the size of from about 5 to 100 microns with a major portion, e.g. in excess of 50% by weight, thereof being in the range of from 40 to 80 microns. The specific transport velocity is selected so as to minimize slippage of the catalyst and yet provide sufficient residence time within the riser tube in order to realize the optimum degree of conversion of a particular hydrocarbon feedstock. Also, it was indicated that using various tapered elongated conduits permits a method for controlling residence time within the elongated tubular conduit.
U.S. Pat. No. 4,219,407 (1980) assigned to Mobil Oil Corporation discloses a riser cracking operation wherein an improved method for separating vapors from entrained catalyst solids is employed. A mixture of vapors and particulates which have been induced to exit from a riser reactor zone are induced to flow outwardly then downwardly. A curved surface causes the particulates of an effluent from the riser to concentrate along this surface. The process is very similar to that disclosed in U.S. Pat. No. 4,313,910.
In U.S. Pat. No. 4,295,961 (1981) of Fahrig et al, there is disclosed a method and apparatus for fluid catalytic cracking wherein a direction of a mixture of fluid and particulate matter is induced to travel in a downward direction after exiting from a riser reactor. The mixture moving in a downward path has a ballistic separation performed on the downwardly flowing mixture of particles and vapor. The particles and vapor have been in part concentrated through a cyclonic induced separation wherein some of the particles have been induced to move in a curved path which likely causes some of the particulate components to concentrate along the wall defining the curved path.
In U.S. Pat. No. 4,310,489 (1982) of Fahrig et al, there is disclosed a separation of a fluid stream comprising a mixture of particulates and vapors which involves both a ballistic and cyclonic separation. From a riser cracker, a mixture comprising particulates and vapors reverses direction and flows downwardly prior to transverse movement of vapors away from particulates into a cyclone.
In U.S. Pat. No. 4,313,910 (1980) of Dries et al, there is disclosed an apparatus for separating a carrier gas from a particle/carrier gas stream. It is particularly adaptable to reactor-risers commonly used in catalytic cracking of hydrocarbon feedstocks. The separation is basically a cyclonic separation wherein a mixture of a carrier gas and particulate matter are accelerated along a curved surface so as to induce the particles to concentrate along the curved surface. Additionally, there is added a substitute fluid through one or more apertures in the curved surface in order to substantially replace the carrier gas remaining in the spaces between the particles. As is clear from catalytic cracking of hydrocarbons, the carrier fluid consists of cracked products and the substitute fluid, of uncracked hydrocarbons. A cleaner separation of catalyst particles from the carrier stream is asserted. The exiting particulate stream relative to its incoming stream from the riser cracker for example can be any where from 90 degrees to about 180 degrees. The fluid stream is moved laterally relative to the mixture of the particulate and carrier streams. The separation disclosed in U.S. Pat. No. 4,313,910 is clearly cyclonic.
U.S. Pat. No. 4,318,800 (1982) assigned to Stone and Webster Engineering Corporation discloses an improved thermal regenerative cracking apparatus and process. Separator efficiency was improved by causing vapor components to move in a flow path involving a 180 degree turn. Further it was disclosed that the flow path must be essentially rectangular and the relationship between barrier height and the sharpness of the U-bend in the gas flow was very significant.
In U.S. Pat. No. 4,341,624 (1982) of George D. Myers, there is disclosed the use of a ballistic separation in a reduced crude conversion process. The importance of this disclosure was that use of ballistic separation in a riser similar to a riser conventionally used in a fluid catalytic cracking system could be carried out in the context of the types of hydrocarbons catalysts and superficial velocities of vapors and solid mixtures in such an elongated conduit. Carbo-metallic feeds employed in the invention involve a 343.degree. C. (650.degree. F.) plus material containing at least 4 parts per million of nickel equivalents as defined in its specification.
In U.S. Pat. No. 4,390,503 (1983) of P. W. Walters et al, there is disclosed a ballistic separation device and method where the flow path of a mixture of particulate matter and vapors are separated into a stream of particulate matter and a stream of substantially only vapor components. It is primarily a ballistic separation because the particulate matter entrained within the mixture of particulate matter and vapor does not change speed or velocity relative to the mixture prior to having vapor components laterally drawn off from the mixture. Also disclosed is a target against which the mixture can impinge. The target causes some cyclonic motion which occurs substantially after vapor components have been separated. Vapor components are initially separated from the mixture of particulate and vapor components prior to contact of the target by the particulate components. The path of the vapors in U.S. Pat. No. 4,390,503 usually involves at least one 180 degree turn after exiting from a conduit and before entering into a cyclone or cyclonic separation system. This is primarily a ballistic separation with a minor amount of cyclonic separation.
U.S. Pat. No. 4,394,349 (1983) assigned to Standard Oil Company (Indiana) disclosed an apparatus for fluidized catalytic cracking of a hydrocarbon feedstock. The apparatus involves a riser reactor and a collar positioned about the axis defined by the downstream end of the reactor. The collar is positioned in close proximity to, but not in contact with, the riser reactor so that an annular space is defined between the riser reactor and the collar. The collar has a diameter greater than the diameter of the riser, but is spaced away from the riser so as not to be in contact with the riser in order to avoid expansion problems. Two significant differences between the riser disclosed in U.S. Pat. No. 4,394,349 and the instant invention are:
1. the relationship between a coanda influenced vapor stream entering through passageway 45 and the vapor/particulate stream flowing through riser 44 (see FIGS. 2-6); and
2. the influence of the pressure drop across a cyclone upon vapor components from within the riser 44 to cyclone separation means 46. These differences will be discussed in more detail later in this specification when specific embodiments of the instant invention are discussed.
U.S. Pat. No. 4,477,335 (1984) of Roger M. Benslay assigned to Ashland Oil, Inc., discloses a method and apparatus for two stage regeneration in which a downcomer within a regenerator vessel causes downward transfer from an upper section to a lower section. As catalyst is transferred from the upper section to the lower sections a ballistic type separation is carried out.
Great Britain Ser. No. 816,550 (1958) discloses apparatus for separation of solid particulates from a gas stream in which they are entrained. A ballistic type separation is disclosed wherein vapors are drawn off from a chamber which surrounds at least a portion of a conduit which is similar to appearance to a riser.
It is an object of this invention to provide improved separation by way of ballistic separation which involves use of a progressive flow reactor.
Other objects of this invention will be clear based upon the disclosure made herein.